Predrying tunnels for mill drying devices

ABSTRACT

A predrying tunnel for the combustion chamber of a steam generator in which the cooling pipes of the steam generator comprise the walls of predrying tunnels and are arranged horizontally in a vertical superimposed array. The cooling pipes forming the walls of the predrying tunnels extend from gas port inlets at the top of the tunnels downwardly to the level of injection of coal into the predrying tunnels. Hot gases are drawn from the combustion chamber of the steam generator through the predrying tunnels to dry wet coal injected into the tunnel before it drops to a plurality of mills which pulverize the coal. A plurality of blowers coupled to the predrying tunnels draws the pulverized coal and gases from the tunnel and mills, and forces the gases and coal through the burners of the steam generator into the combustion chamber where the coal is ignited.

United States Patent [1 1 Kuhn [ 1 July 24, 1973 PREDRYING TUNNELS FORMILL DRYING DEVICES [75] Inventor: Rudolf Kuhn, Oberhausen, Germany [73]Assignee: Deutsch Babcock & Wilcox Aktiengesellschatt,Oberhausen/Rhineland, Germany [22] Filed: May 11, 1972 [21] Appl. N0.:252,447

[30] Foreign Application Priority Data 9/1966 Wiechard et a]. 110/106 XPrimary Examiner-Kenneth W. Slprague Attorney-Allis0n C. Collard [57]ABSTRACT A predrying tunnel for the combustion chamber of a steamgenerator in which the cooling pipes of the steam generator comprise thewalls of predrying tunnels and are arranged horizontally in a verticalsuperimposed array. The cooling pipes forming the walls of the predryingtunnels extend from gas port inlets at the top of the tunnels downwardlyto the level of injection of coal into the predrying tunnels. l-lotgases are drawn from the combustion chamber of the steam generatorthrough the predrying tunnels to dry wet coal injected into the tunnelbefore it drops to a plurality of mills which pulverize the coal. Aplurality of blowers coupled to the predrying tunnels draws thepulverized coal and gases from the tunnel and mills, and forces thegases and coal through the burners of the steam generator into thecombustion chamber where the coal is ignited.

7 Claims, 4 Drawing Figures Patented July 24, 1973 3,747,571

2 Sheets-Sheet 1 Patented July 24,1973 3,747,571

2 Sheets-Sheet 2 Fig. 2

PREDRYING TUNNELS FOR MILL DRYING DEVICES The present invention relatesto steam generators, and in particular, to pipe-cooled predrying tunnelsfor a mill-drying device of the coal dust furnace type.

Predrying tunnels for steam generators are known in the prior art. Seefor example, West German Patent No. 969,609. Predrying tunnels, such asthese, are generally disposed outside of the steam generator combustionchamber, and exhaust ports are provided in the combustion chamber wallsto channel gases from the combustion chamber to the predrying tunnels.In order to cool these predrying tunnels, some of the pipes used to coolthe combustion chamber of the steam generator are mounted on the innersurfaces of the predrying tunnels. The cooling pipes of each tunnelextend through openings in the combustion chamber cooling pipe wall, sothat many co'oling pipes may be used to cool the tun nels.

The above-described cooling pipe structure for the predrying tunnels isdisadvantageous since the cooling pipes are heated asymmetrically whenthe mill-drying device is run at a low capacity, or when the mill-dryingdevice is not operated. This asymmetrical heating of the cooling pipesoccurs over the cooling area of each predrying tunnel, which extendsfrom its combustion chamber gas inlet port to the level at which coal isinjected into the predrying tunnel. In a continuously operating steamgenerator, the flow generated into steam by the steam generator issensitive when the milldrying device operates at a low capacity, andcould possibly become instable. Asymmetrical admittance of heat to thecooling pipes is, thus, not desirable, and the predrying tunnel coolingpipes are limited to the exhaust outlet area of each tunnel, since thecooling pipes are heated by the flame of the furnace of the steamgenerator directly only at that area of the tunnels. It is not possible,therefore, to cool that portion of the predrying tunnels between theexhaust outlet of the tunnels and the level at which the coal isinjected into the tunnels.

It is therefore an object of the present invention to provide apredrying tunnel for a mill-drying device of a steam generator in whichthe area of the predrying tunnels between the exhaust outlet thereof andthe level of injection of the fuel thereinto is cooled during operationof the steam generator.

it is also an object of the present invention to provide a predryingtunnel for a mill-drying device of a steam generator in which thecombustion chamber cooling pipes of the steam generator absorb heatgenerated in equal amounts while the mill-dryingdevice operates at a lowcapacity.

'It is still another object of the present invention to provide apredrying tunnel for a mill-drying device of a steam generator which issimple in design, easy to manufacture and efficient and reliable in itsoperation.

Accordingly, the present invention provides a predrying tunnel for amill-drying device of a steam generator in which the cooling pipesutilized to cool the combustion chamber wall of the steam generator aredistributed in equal lengths over the inner walls of the predryingtunnels so that the steam generator flow is channeled through thecooling pipes disposed in the predrying tunnels. Each of the coolingpipes surrounding the combustion chamber of the steam generator anddisposed on the inner walls of the predrying tunnels are continuous andequal in length. Thus, heat is admitted to the cooling pipes in equalamounts, when either one or more of the mill drying devices of thepredrying tunnels are in operation or operate at a low capacity.

In the present invention, all bends in the cooling pipes are equal inlength, and-fewer pipes are required than with conventional predryingtunnels. The cooling pipes are easily manufactured, and since they havean even flow-through resistance, the flow characteristics through thepipes are stable. Furthermore, since the temperature of the coolingpipes in the predrying tunnels and the walls of the combustion chamberis maintained at a constant level, the predrying tunnels may be coupledto the combustion chamber walls and the pipes thereof may be weldedtightly together. This eliminates the requirement of conventionalpredrying tunnels that a special carrier frame be provided for the.tunnels around the combustion chamber.

It should be noted that the predlrying tunnels of the present inventionmay be disposed either inside or outside of the combustion chamber wallsof the steam generator. With either arrangement, the heat loss whichoccurs in the steam generator is less than that which occurs inconventional steam generators in which the predrying tunnels extend intofree space. Furthermore, because of this optional configuration, theconstruction of the boiler frame for the steam generator and themounting of the boiler frame, are both more inexpensive, faster andeasier than with conventional steam generators, and dead angles may beused in the combustion chamber without producing a detrimental effect onthe heat transfer which occurs in the combustion chamber, or on thecombustion chamber flame.

Directing the flow of the steam generator through the cooling pipes ofthe predrying tunnels does not disturb the stability of the steamgenerator flow. The interior spaces of the predrying tunnels areseparated from the combustion chamber by a vertical wall of coolingpipes, and openings are provided on the upper ends of the predryingtunnels to couple the tunnels with the combustionchamber. The tunnelsare not coupled to the combustion chamber at their lower ends.

The wall of cooling pipes separating the combustion chamber from theinterior of the predrying tunnels serves both as a heating face for thecombustion chamber and as a cooling face for the predrying tunnels. Thiswall separating the tunnel and the combustion chamber comprises a'vertical array of two columns of pipes, the number of which is the sameon both sides of the wall.

Each cooling pipe which forms the cooling face of the predrying tunnelshas the same length, so that each pipe forming the cooling face of thepredrying tunnels is heated by the same amount. This constructionprevents instability of the flow of the steam generator. The total flowof the steam generator is channeled through the cooling pipes of thepredrying tunnels in order to prevent instability of the flow caused bya unilateral change in the heating of the wall of cooling pipesseparating the combustion chamber from the interior of the predryingtunnels. With the above-described construction of the predrying tunnels,a single wall of cooling pipes may be utilized to construct a singlepredrying tunnel and separate its interior from the combustion chamberof the steam generator. The width of such a tunnel is designed so thatthe tunnel capacity is sufficient to meet the requirements of the steamgenerator.

Other objects and features of the present invention will become apparentfrom the following detailed description taken in connection with theaccompanying drawings which disclose several embodiments of theinvention. It is to be understood, however, that the drawings aredesigned for the purpose of illustration only and are not intended as adefinition of the limits and scope of the invention.

In the drawings, wherein similar reference characters denote similarelements throughout the several views:

FIG. 1 is a top cross-sectional view of the combustion chamber of asteam generator constructed in accordance with the present invention,taken along section l1 of FIG. 2;

FIG. 2 is a cross-sectional side view of the combustion chamber, takenalong section 2-2 of FIG. 1;

FIG. 3 is an enlarged top cross-sectional view of one embodiment of apredrying tunnel constructed in accordance with the present invention;and

FIG. 4 is an enlarged top cross-sectional view of another embodiment ofa predrying tunnel constructed in accordance with the present invention.

Referring to the drawings, there is shown a vertically disposedcombustion chamber 1 for the steam generator of the present invention.The combustion chamber includes pipe walls 2 which consist of acontinuous length of a pipe 4 coiled in a rectangular shape around thecombustion chamber and superimposed over itself vertically. Thevertically-disposed array of pipes are welded together so as to be gasimpermeable, and are suspended from the upper portion of a boiler frame3. The mounting apparatus 4 of the pipes is known in the art andpresents no problem to persons of ordinary skill in the art. Pulverizedwet coal, such as, for example, bitumen coal, having a water contentgreater than 35 percent, is burned in combustion chamber 1 to produceheat for the steam generator. To facilitate easy burning of the coal,the coal is dried by hot gases drawn from the combustion chamber of thesteam generator, and pulverized in a mill, before it is injected intothe combustion chamber of the steam generator. Hot gases produced by theflames in the combustion chamber of the steam generator are drawn fromthe combustion chamber through predrying tunnels to the mill used topulverize the coal. The coal to be burned in the combustion chamber isalso drawn through the predrying tunnels to the mill so that the wetcoal is dried while it drops through the tunnels. Hence, these tunnelsare known by those skilled in the art as predrying tunnels in amilldrying device." Suction blowers draw the hot gases from thecombustion chamber and force the gases and the pulverized coal to themill. From there, the gases and coal are forced through burners into thecombustion chamber where the coal is ignited.

The predrying tunnels of the present invention are cooled by a pluralityof continuous cooling pipes, through which the flow of the steamgenerator is channeled, between the gas intake ports of the tunnels andthe level of the predrying tunnels at which the wet coal is injectedinto the tunnels to be dried by the gases as it drops downwardly towardsthe mills. As shown in FIG. 1, continuous pipe 4 forms a combustionchamber wall through which the steam-water mixture of the steamgenerator flows in the direction of arrow 5. Pipe 4 is coiled aroundcombustion chamber 1 in a continu' ous spiral, and is bent to formsections 6 and 7. Continuity of the pipe is maintained through thesebends. In

FIG. 2, the cooling pipes have not been illustrated to preserve clarityof the drawings.

As shown in detail in FIG. 3, pipe 4 is bent to form sections 6, whichare of equal length. Sections 6 form a vertical wall comprising twoadjacent columns of pipes welded at one end to the wall of pipes aroundthe combustion chamber so as to form a plurality of predrying tunnels 8.Sections 7 of the pipe, disposed adjacent heat insulation material 20,form the outer walls of predrying tunnels 8 and are also equal inlength. Instability in the flow of the steam-water mixture of the steamgenerator is prevented by insuring that the pipe sections are of equallength. The entire flow of the steam-water mixture of the steamgenerator is channeled through cooling pipe sections 6 and 7 of thepredrying tunnels.

Hot gases produced by the flame in the combustion chamber are drawn offby gas intake ports 9 which are coupled to the upper portions ofpredrying tunnels 8. The lower ends of the predrying tunnels are notcoupled to the combustion chamber and are closed off by plates 10.Predrying tunnels 8 are coupled to lateral tunnels 11 in which the wetcoal is injected by feeding means 12, which may be a chute. Predrying ofthe coal begins as the wet coal drops through tunnel sections 13. Thecoal drops into mills 14, which are paddle mills, for furtherpulverization and drying. The mills also include larger paddle wheels 15which also pulverize the coal, and draw out the gas and the coal dustfrom mills l4.

Paddle wheels 15 draw the hot gases from the combustion chamber 1through ports 9, tunnels 8, l1 and 13 into mills l4. Tunnels 8 arecooled by the cooling pipes as the gases are drawn therethrough. Thepulverized, dried coal is forced by paddle wheels 15 upwardly throughfeed pipes 16 to burners 17, which inject the coal into combustionchamber 1 with the cooled gases. Air is fed to burners 17 through airfeed pipes 18 to aid in the combustion and ignition of the pulverizedcoal. Air supply couplings 19 are also coupled to tunnel sections 13 toregulate the drying temperature by admitting cool air in controlledamounts.

The predrying tunnels are constructed wide enough so that each maybeprovided with two predrying tunnel sections 11 and 13 and twomill-drying and blower devices 14 and 15. The amount of the coal dustand gas which is injected by burners 17 into combustion chamber l isadjusted by regulating the air supply to each of the predrying tunnelsand burners. Thus, the apparatus may be adjusted to compensate for theeffects produced when one or more of mills 14 is inoperative oroperating at a low capacity. And, although the heating of cooling pipes6 and 7 in the predrying tunnels is different, heat is admitted in equalamounts to pipe walls 2 between cooling pipes 6 and 7 since each of thepipe walls is of the same length. The superimposed arrangement of thecooling pipes between the predrying tunnels also distributes theirregularities of the heating process to the total length of pipe 4.

In FIG. 4, another embodiment of a predrying tunnel is disclosed. Inthis embodiment, pipe 4 is bent in a circular coil and is disposedwithin the heat insulation material 20 of pipe walls 2. Predryingtunnels 8 formed by these coils are substantially the same as theabovedescribed predrying tunnels. Tunnels 8 comprise a plurality ofcircular coils superimposed upon each other, each coil being of the samelength to prevent instability of the flow through the cooling pipes.

The materials used to construct the steam generator combustion chamberdescribed above may be of any suitable conventional type. Selection ofthese materials will present no problem to those persons skilled in theart.

When predrying tunnels are constructed in accordance with the presentinvention, it is not necessary to provide a fire-proof lining or casingfor the interior of the tunnels. Slag also does not form on the walls ofthe predrying tunnels, and the air flow between the walls does not,therefore, become constricted. The predrying tunnels are mounted on themounting frame of the steam generator along with pipe walls 2, and thusdo not require separate mounting means. The heat loss of a combustionchamber constructed as described above is also reduced since thepredrying tunnels are encompassed in the heat insulation material 20 ofthe steam generator combustion chamber.

The temperature of the hot gases drawn off from the combustion chamberfor drying the wet coal is lowered by the admittance of cool air bycoupling 19, without any additional air supply, to a temperature whichis compatible with the materials of the mills 14. Dead angles also maybe used for the predrying tunnels, and as a result, combustion chamber 1may be constructed as a vertically rotating burner chamber ofrectangular shape.

Cooling pipe sections 6 and 7 of the predrying tunnels form heatingfaces which reduce the heat in combustion chamber 1 and prevent thesteam-water mixture flowing through pipe walls 2 from completelyevaporating. When the mills are operating at a low load capacity, i.e.,when one or more of the mills are switched off, cooling pipe sections 6and 7 function as unheated throttle areas so that sections of pipe 4within pipe walls 2 are heated more intensely and move evenly and theflow stability of the steam-water mixture is improved. As a result ofthis improvement of the flow stability during operation of the mills atlow load capacity, mills 14 are operated more economically. With the ap'paratus of the present invention, no disadvantages are present if one ormore of the entire group of mills 14 is completely shut off while theremainder of themills work at full load capacity. Furthermore, in orderto regulate the flow through the steam generator, it is no longernecessary with the apparatus of the present invention to evenlydistribute the capacity to all of mills l4.

While only several embodiments of the present invention havebeen shownand described, it will be obvious to those persons skilled in the artthat many changes and modifications may be made thereunto withoutdeparting from the spirit and scope of" the invention.

What is claimed is:

I. A predrying tunnel for the combustion chamber of a steam generator,comprising:

a plurality of horizontally disposed, vertically superimposed, coolingpipes, disposed in spiral arrangement around the combustion chamber ofthe steam generator, said spiral arrangement of said pipes comprisingone continuous pipe length and forming pipe walls on the interiorsurfaces of the combustion chamber,.and being bent at at least onecorner of the combustion chamber so as to form at least one verticaltunnel within the combustion chamber of the steam generator;

means, coupled to said vertical tunnel, for guiding gases from thecombustion chamber to said tunnel;

at least one additional cylindrical tunnel coupled to said verticaltunnel in the combustion chamber;

means, for injecting fuel into said cylindrical tunnel;

and

means, coupled to saidcylindrical tunnel, and to the combustion chamber,for pulverizing fuel injected into said cylindrical tunnel, and drawingair from the combustion chamber through said vertical tunnel and saidcylindrical tunnel and forcing said air and pulverized fuel into thecombustion chamber of the steam generator.

2. The predrying tunnel as recited in claim 1, wherein said verticaltunnel is triangular in shape, one wall of said vertical tunnelcomprising at least two adjacent vertical walls of superimposed pipesfor separating the combustion chamber from the interior of said verticaltunnel.

3. The predrying tunnel as recited in claim 2, wherein said fuelpulverizing means comprises a paddle wheel mill, disposed at the bottomof said cylindrical tunnel, for pulveriz ing fuel injected into saidcylindrical tunnel.

4. The predrying tunnel as recited in claim 3, wherein said paddle wheelmill further comprises blower means, for drawing gases from thecombustion chamber through said vertical tunnel and said cylindricaltunnel into said mill, and forcing the pulverized fuel and said gasesinto the combustion chamber of the steam generator.

5. The predrying tunnel as recited in claim 4, wherein said cylindricaltunnel is coupled to the combustion chamber of the steam generator by aplurality of elongated pipes and combustion chamber burners which guidethe gases and pulverized fuel from said mill to the combustion. chamber.

6. The predrying tunnel as recited in claim 1, wherein said .verticaltunnel is circular in shape, and comprise a vertically disposed array ofhorizontal coils.

7. The predrying tunnel as recited in claim 1, wherein said coolingpipes comprising the'walls of said vertical tunnel are disposed betweenthe points at which said cylindrical tunnel and said means forguidinggases from the combustion chamber into said vertical tunnel are coupledto said vertical tunnel.

1. A predrying tunnel for the combustion chamber of a steam generator,comprising: a plurality of horizontally disposed, verticallysuperimposed, cooling pipes, disposed in spiral arrangement around thecombustion chamber of the steam generator, said spiral arrangement ofsaid pipes comprising one continuous pipe length and forming pipe wallson the interior surfaces of the combustion chamber, and being bent at atleast one corner of the combustion chamber so as to form at least onevertical tunnel within the combustion chamber of the steam generator;means, coupled to said vertical tunnel, for guiding gases from thecombustion chamber to said tunnel; at least one additional cylindricaltunnel coupled to said vertical tunnel in the combustion chamber; means,for injecting fuel into said cylindrical tunnel; and means, coupled tosaid cylindrical tunnel, and to the combustion chamber, for pulverizingfuel injected into said cylindrical tunnel, and drawing air from thecombustion chamber through said vertical tunnel and said cylindricaltunnel and forcing said air and pulverized fuel into the combustionchamber of the steam generator.
 2. The predrying tunnel as recited inclaim 1, wherein said vertical tunnel is triangular in shape, one wallof said vertical tunnel comprising at least two adjacent vertical wallsof superimposed pipes for separating the combustion chamber from theinterior of said vertical tunnel.
 3. The predrying tunnel as recited inclaim 2, wherein said fuel pulverizing means comprises a paddle wheelmill, disposed at the bottom of said cylindrical tunnel, for pulverizingfuel injected into said cylindrical tunnel.
 4. The predrying tunnel asrecited in claim 3, wherein said paddle wheel mill further comprisesblower means, for drawing gases from the combustion chamber through saidvertical tunnel and said cylindrical tunnel into said miLl, and forcingthe pulverized fuel and said gases into the combustion chamber of thesteam generator.
 5. The predrying tunnel as recited in claim 4, whereinsaid cylindrical tunnel is coupled to the combustion chamber of thesteam generator by a plurality of elongated pipes and combustion chamberburners which guide the gases and pulverized fuel from said mill to thecombustion chamber.
 6. The predrying tunnel as recited in claim 1,wherein said vertical tunnel is circular in shape, and comprise avertically disposed array of horizontal coils.
 7. The predrying tunnelas recited in claim 1, wherein said cooling pipes comprising the wallsof said vertical tunnel are disposed between the points at which saidcylindrical tunnel and said means for guiding gases from the combustionchamber into said vertical tunnel are coupled to said vertical tunnel.